A growing number of microscopy experiments involve photomanipulation where light is directed to a subset of the sample that is being imaged. For example, a field of labeled cells could be imaged where it is desirable that one of the many cells is illuminated with a specific wavelength of light while the other cells are not. Fluorescence recovery after photobleaching (FRAP) would be a common example of this technique. Other examples include photo-uncaging, photo-stimulation, ablation, photo-wounding, or limiting the excitation field so that some parts of the imaged field are excluded. There are several available devices for building a photomanipulation system, the most common being galvo-scanners, digital light projectors (DLP), and spatial light modulators (SLM)—hereafter referred to as projection devices.
In specific fields of microscopy, for example optogenetics, there is a need to simultaneously illuminate several spots. A scanning system is inconvenient for this because it would require a different scanner for each spot. The only current commercially available products are DLP and SLM devices that can accomplish this task.
A DLP device masks unwanted areas from being illuminated by redirecting the light from those areas. This means that the intensity at any one spot is the intensity of the input illumination divided by the fraction of the area of the spot. This means that for any given input illumination, the relative intensity is low at one spot. DLP devices have the advantage however that they always have uniform intensity density regardless of the area being illuminated.
SLM devices have nearly opposite characteristics. When illuminating a single spot, all of the input illumination goes to that spot, that is, the total intensity remains the same regardless of the illuminated area. However, in SLM devices, the intensity density is dependent on the area.
For certain applications, significant power is needed at a spot to cause the desired photomanipulation. DLP devices with any practical input illumination are unable to provide the required intensity density. Thus for certain applications an SLM device is desired.
For even more specific applications, there may be a need for multiple wavelength photomanipulation. For DLP and SLM projection devices this means that a separate device is used for each desired wavelength.
For other specific applications, there is required fast, precise timing between illumination of several spots. For example, one neuron needs to be stimulated exactly 1 millisecond after another neuron is stimulated. This means that the light pattern must change within that millisecond. Unfortunately, most available commercial SLM devices cannot change their patterns that fast.
An exemplary embodiment describes an SLM device that can simultaneously illuminate different spots with different wavelengths. The exemplary embodiment can also illuminate different spots with fast precise timing between the different illumination patterns.